1. Field of the Invention
The invention relates to a vehicle frame component used as a frame of a vehicle component, such as a vehicle seat frame and a vehicle body frame, and a manufacturing method for the vehicle frame component.
2. Description of Related Art
In recent years, there are known vehicles as typified by minivans, in which three rows of vehicle seats are arranged in the vehicle longitudinal direction. Among these three-row vehicle seats, the third-row seat is arranged behind the second-row seat. At the third-row seat, a knee space for an occupant seated in the third-row seat is likely to be narrow. Therefore, it is desirable that a widest possible knee space be ensured for an occupant seated in the third-row seat. Accordingly, there is a known back frame of such a second-row seat, which is curved rearward in an arcuate shape from a lower back portion toward a back portion (for example, see Japanese Patent Application Publication No. 2010-131640 (JP 2010-131640 A)). When the back frame is curved to be bowed in an arcuate shape in this way, it is possible to arrange the lower back portion of the second-row seat forward. Therefore, it is possible to increase the knee space for an occupant seated in the third-row seat. Note that the back frame is curved rearward such that the back frame is bowed in an arcuate shape from the lower back portion toward the back portion, through a drawing process in press working. Specifically, a steel sheet is deformed into a curved shape of the back frame by drawing the steel sheet such that the steel sheet is bowed in an arcuate shape through the drawing process in press working.
Note that, nowadays, a high-tensile steel sheet having an extremely high strength is more likely to be selected as the material of a vehicle frame component, such as the above-described back frame. Because such a high-tensile steel sheet has an extremely high strength, if the high-tensile steel sheet is subjected to the above-described drawing process to be bowed in an arcuate shape, wrinkles are formed in the high-tensile steel sheet. Once wrinkles are formed in the high-tensile steel sheet in this way, the wrinkles may interfere with another component or the wrinkles may decrease the strength of the vehicle frame component. Therefore, formation of such wrinkles in the vehicle frame component should be avoided.